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The middle-ear system relies on a balance of mass and stiffness characteristics for transmitting sound from the external environment to the cochlea and auditory neural pathway. Phase is one aspect of sound that, when transmitted and encoded by both ears, contributes to binaural cue sensitivity and spatial hearing. The study aims were (i) to investigate the effects of middle-ear stiffness on the auditory brainstem neural encoding of phase in human adults with normal pure-tone thresholds and (ii) to investigate the relationships between middle-ear stiffness-induced changes in wideband acoustic immittance and neural encoding of phase. The auditory brainstem neural encoding of phase was measured using the auditory steady-state response (ASSR) with and without middle-ear stiffness elicited via contralateral activation of the middle-ear muscle reflex (MEMR). Middle-ear stiffness was quantified using a wideband acoustic immittance assay of acoustic absorbance. Statistical analyses demonstrated decreased ASSR phase lag and decreased acoustic absorbance with contralateral activation of the MEMR, consistent with increased middle-ear stiffness changing the auditory brainstem neural encoding of phase. There were no statistically significant correlations between stiffness-induced changes in wideband acoustic absorbance and ASSR phase. The findings of this study may have important implications for understanding binaural cue sensitivity and horizontal plane sound localization in audiologic and otologic clinical populations that demonstrate changes in middle-ear stiffness, including cochlear implant recipients who use combined electric and binaural acoustic hearing and otosclerosis patients.

Neurodevelopmental disorders are on the rise worldwide, with diagnoses that detect derailment from typical milestones by 3-4.5 years of age. By then, the circuitry in the brain has already reached some level of maturation that inevitably takes neurodevelopment through a different course. There is a critical need then to develop analytical methods that detect problems much earlier and identify targets for treatment. We integrate data from multiple sources, including neonatal auditory brainstem responses (ABR), clinical criteria detecting autism years later in those neonates, and similar ABR information for young infants and children who also received a diagnosis of autism spectrum disorders, to produce the earliest known digital screening biomarker to flag neurodevelopmental derailment in neonates. This work also defines concrete targets for treatment and offers a new statistical approach to aid in guiding a personalized course of maturation in line with the highly nonlinear, accelerated neurodevelopmental rates of change in early infancy.Significance StatementAutism is currently detected on average after 4.5 years of age, based on differences in social interactions. Yet basic building blocks that develop to scaffold social interactions are present at birth and quantifiable at clinics. Auditory Brainstem Response tests, routinely given to neonates, infants, and young children, contain information about delays in signal transmission important for sensory integration. Although currently discarded as gross data under traditional statistical approaches, new analytics reveal unambiguous differences in ABR signals’ fluctuations between typically developing neonates and those who received an autism diagnosis. With very little effort and cost, these new analytics could be added to the clinical routine testing of neonates to create a universal screening tool for neurodevelopmental derailment and prodrome of autism.

We integrated data from a newborn hearing screening database and a preschool disability database to examine the relationship between newborn click evoked auditory brainstem responses (ABRs) and developmental disabilities. This sample included children with developmental delay (n = 2992), speech impairment (SI, n = 905), language impairment (n = 566), autism spectrum disorder (ASD, n = 370), and comparison children (n = 128,181). We compared the phase of the ABR waveform, a measure of sound processing latency, across groups. Children with SI and children with ASD had greater newborn ABR phase values than both the comparison group and the developmental delay group. Newborns later diagnosed with SI or ASD have slower neurological responses to auditory stimuli, suggesting sensory differences at birth.

Previous studies report prolonged auditory brainstem response (ABR) in children and adults with autism spectrum disorder (ASD). Despite its promise as a biomarker, it is unclear whether healthy newborns who later develop ASD also show ABR abnormalities. In the current study, we extracted ABR data on 139,154 newborns from their Universal Newborn Hearing Screening, including 321 newborns who were later diagnosed with ASD. We found that the ASD newborns had significant prolongations of their ABR phase and V-negative latency compared with the non-ASD newborns. Newborns in the ASD group also exhibited greater variance in their latencies compared to previous studies in older ASD samples, likely due in part to the low intensity of the ABR stimulus. These findings suggest that newborns display neurophysiological variation associated with ASD at birth. Future studies with higher-intensity stimulus ABRs may allow more accurate predictions of ASD risk, which could augment the universal ABR test that currently screens millions of newborns worldwide. LAY SUMMARY: Children with autism spectrum disorder (ASD) have slow brain responses to sounds. We examined these brain responses from newborns' hearing tests and found that newborns who were later diagnosed with autism also had slower brain responses to sounds. Future studies might use these findings to better predict autism risk, with a hearing test that is already used on millions of newborns worldwide.

We present a surgical technique of closed tympanoplasty for chronic otitis, together with an intraoperative functional evaluation system with the OssiMon LAIOM software. The technique can be used in one or two steps for an intraoperative evaluation of the functional effect during ear operation. Using OssiMon LAIOM, we were able to simultaneously measure the auditory steady-state response (ASSR), as well as to perform laser dopler vibrometry (LDV). For electrophysiologic measurements, OssiMon LAIOM uses the Intelligent Hearing System platform, and the Polytec single-point laser to evaluate the ossicular mobility. The measurements can be conducted using both methods at the same time or separately, applying each method independently. The OssiMon LAIOM software records the ASSR response intraoperatively and marks it automatically on the audiogram with the preoperative hearing level. The ossicular vibration level is determined based on the measured LDV response. To the best of our knowledge, OssiMon LAIOM is the first solution allowing to objectively measure the effectiveness of tympanoplasty using two methods simultaneously, i.e. ASSR and LDV. The system could be widely applied in the functional evaluation of the middle ear and in clinical practice.

OBJECTIVES Using the continuous loop averaging deconvolution (CLAD) technique for conventional electrocochleography (ECochG) and auditory brainstem response (ABR) recordings, the effects of testing at high stimulus rates may have the potential to diagnose disorders of the inner ear and auditory nerve. First, a body of normative data using the CLAD technique must be established. DESIGN Extratympanic click ECochG and ABR to seven stimulus rates using CLAD were measured simultaneously from a tympanic membrane electrode and surface electrodes on the forehead and mastoid of 42 healthy individuals. RESULTS Results showed that the compound action potential (AP) of the ECochG and waves I, III, and V of the ABR decreased in amplitude and increased in latency as stimulus rate was increased from standard 7.1 clicks/s up to 507.81 clicks/s, with sharp reduction in AP amplitude at 97.66 clicks/s and reaching asymptote at 292.97 clicks/s. The summating potential (SP) of the ECochG, however, stayed relatively stable, resulting in increased SP/AP ratios with increasing rate. The SP/AP amplitude ratio showed more stability than AP amplitude findings, thus it is recommended for use in evaluation of cochlear and neural response. CONCLUSIONS Results of both amplitude and latency data from this normative neural adaptation function of the auditory pathway serves as guide for improving diagnostic utility of both ECochG and ABR using CLAD as a reliable technique in distinguishing inner ear and auditory nerve disorders.

PurposeThe purpose of this study was to measure magnitude changes of auditory steady-state responses (ASSRs) and respective transient middle- and long-latency responses as a function of stimulus intensity and carrier frequency. The literature lacks clear consensus, including relationship to loudness.MethodA cohort of 48 adults with normal hearing was examined from a companion study (Tlumak, Durrant, & Delgado, 2015) on effects of aging. ASSRs were elicited by repeated tone-burst stimuli presented at rates of 40 and 0.75 Hz at 3 frequencies and 5 levels of stimulus intensity. The design also permitted scrutiny of any gender bias to the results.ResultsSimilar to derived transient response findings, ASSR magnitude (harmonic sum) systematically increased with intensity. Input–output function only at 0.75 Hz approximated a log–log linear function. However, slopes fell well below that of doubling of loudness per 10 dB SPL. Results failed to demonstrate significance as a function of carrier frequency and gender for both repetition rates.ConclusionEffects of stimulus intensity, carrier frequency, and gender on ASSRs were similar to those of their transient counterparts. Findings remain disappointing for objective loudness estimation. Results suggest only a clear linkage to the long-latency response and the 0.75-Hz magnitude but require careful consideration of limitations/underlying mechanisms when measuring loudness-related effects.

The effects of rate on auditory-evoked potentials (AEP) to short noise gaps (12 ms) recorded at high sampling rates using wide-band filters were investigated.Auditory brainstem (ABR), middle latency (MLR), late latency (LLR) and steady-state (ASSR) responses were simultaneously recorded in adult subjects at four gap rates (0.5, 1, 5 and 40 Hz). Major components (V, Na, Pa, Nb, Pb, N1 and P2) were identified at each rate and analysed for latency/amplitude characteristics. Gap responses at 40 Hz were recovered from Quasi-ASSRs (QASSR) using the CLAD deconvolution method.Fourteen right ears of young normal hearing subjects were tested.All major components were present in all subjects at 1 Hz. P1 (P50) appeared as a low-pass filtered component of Pa and Pb waves. At higher rates, N1 and P2 disappeared completely while major ABR-MLR components were identified. Peak latencies were mostly determined by noise onsets slightly delayed by offset responses.Major AEP components can be recorded to short gaps at 1 Hz using high sampling rates and wide-band filters. At higher rates, only ABR and MLRs can be recorded. Such simultaneous recordings may provide a complete assessment of temporal resolution and processing at different levels of auditory pathways.

Electrocochleography (ECochG) to high repetition rate tone bursts may have advantages over ECochG to clicks with standard slow rates. Tone burst stimuli presented at a high repetition rate may enhance summating potential (SP) measurements by reducing neural contributions resulting from neural adaptation to high stimulus repetition rates. To allow for the analysis of the complex ECochG responses to high rates, we deconvolved responses using the Continuous Loop Averaging Deconvolution (CLAD) technique. We examined the effect of high stimulus repetition rate and stimulus duration on SP amplitude measurements made with extratympanic ECochG to tone bursts in 20 adult females with normal hearing. We used 500 Hz and 2000 Hz tone bursts of various stimulus durations (12 ms, 6 ms, 3 ms) and repetition rates (five rates ranging from 7.1/s to 234.38/s). A within-subject repeated measures (rate x duration) analysis of variance was conducted. We found that, for both 500 Hz and 2000 Hz stimuli, the mean deconvolved SP amplitudes were larger at faster repetition rates (58.59/s and 97.66/s) compared to slower repetition rates (7.1/s and 19.53/s), and larger at shorter stimulus duration compared longer stimulus duration. Our concluding hypothesis is that large SP amplitude to short duration stimuli may originate primarily from neural excitation, and large SP amplitudes to long duration, fast repetition rate stimuli may originate from hair cell responses. While the hair cell or neural origins of the SP to various stimulus parameters remains to be validated, our results nevertheless provide normative data as a step toward applying the CLAD technique to understanding diseased ears.

In this paper, a complete integrated method of intraoperative monitoring of hearing (IOMH) during ossiculoplasty performed via posterior tympanotomy is presented. The method integrates auditory steady state responses (ASSR) with Laser-Doppler Vibrometry (LDV) and allows intraoperative optimization of ossicular prosthesis positioning and coupling. Both ASSR and LDV are acquired simultaneously. The results of the integrated measurements are analyzed and evaluated automatically on-line which makes this strategy unaffected by individual differences in interpretations of collected recordings. The technique of intraoperative monitoring of hearing, presented in this paper, allows optimal placement of the prosthesis and replacement if needed as well as confirmation of the ossiculoplasty efficiency by intraoperatively defined hearing threshold and air-bone gap closure before the end of surgery. This article is protected by copyright. All rights reserved.

SignalMaster is a portable open speech and signal processing system that was developed specifically for researchers interested in developing their own real-time signal processing strategies. The system can be used for a wide range of research applications including development of hearing aid amplification and processing strategies and recording of evoked responses. SignalMaster uses a TMS320C6748 Digital Signal Processor (DSP) and provides two input and two output channels with 32 bit Analog-to-Digital (AD) and Digital-to-Analog (DA) convertors. Lithium-ion batteries provide up to 10 hours of freestanding operation. The system is available in two hardware platforms, the standard SignalMaster and the new SignalMasterLite, more compact and light weight for portable applications. The system may also be used while connected to a personal computer (PC) or Android Table via Bluetooth for additional control of experiments, off-line processing and data storage. A DLL provides functions for user developed applications to communicate with the hardware and be upload C language programs. This allows for different applications to be uploaded in order to reconfigure the processing algorithms being executed for any experiment at any time. DSP, PC-based and Android Table software source code examples provide users with the ability to develop their own user specific applications.SignalMaster is a portable open speech and signal processing system that was developed specifically for researchers interested in developing their own real-time signal processing strategies. The system can be used for a wide range of research applications including development of hearing aid amplification and processing strategies and recording of evoked responses. SignalMaster uses a TMS320C6748 Digital Signal Processor (DSP) and provides two input and two output channels with 32 bit Analog-to-Digital (AD) and Digital-to-Analog (DA) convertors. Lithium-ion batteries provide up to 10 hours of freestanding operation. The system is available in two hardware platforms, the standard SignalMaster and the new SignalMasterLite, more compact and light weight for portable applications. The system may also be used while connected to a personal computer (PC) or Android Table via Bluetooth for additional control of experiments, off-line processing and data storage. A DLL provides functions for user developed applicat...

Auditory steady-state responses (ASSR) evoked by recurrent brief tones were assessed over a wide range of stimulus repetition rates apropos the traditionally measured obligatory, transient, auditory evoked potentials. Repetition rates of ≤ 10 Hz have received little attention in the context of the ASSR stimulus-response analysis approach, speculated to provide technical advantages/additional information over more traditional transient stimulus-response paradigms.Magnitudes were measured at repetition rates from 0.75 to 80 Hz, using trains of repeated tone-burst stimuli.Twelve normal-hearing children and a reference sample of 25 young adults.Results show that response magnitudes were significantly larger in children than adults at repetition rates of ≤ 5 Hz. Magnitudes were largest at the two lowest repetition rates, following the trends expected from the transient auditory evoked potential (AEP) literature. The harmonic sum is proposed as a more appropriate measure of response magnitude than amplitude of the fundamental alone.The analysis methods used in this paper may give information that will have applications for clinical testing. Of pragmatic importance is that the stimulus rate profile could be determined without subjective wave identification and/or interpretation, and thus by a method that is inherently more objective than conventional AEP analysis.

Auditory steady-state responses (ASSR) evoked by recurrent tones were assessed over a wide range of stimulus repetition rates embracing well the traditionally measured transient AEPs. Repetition rates of ≤ 10 Hz have received little attention in the context of the ASSR stimulus-response analysis approach which is speculated to provide technical advantages, if not additional/supplemental information, over more traditional transient stimulus-response paradigms.Magnitudes were measured at repetition rates from 0.75 to 80 Hz, using trains of recurrent tone-burst stimuli.Twenty-five normal-hearing adults during sleep and awake.Results show that response magnitudes for adults tested during sleep were significantly larger than those for adults while awake at repetition rates5 Hz. Magnitudes were largest at the two lowest repetition rates, as expected from corresponding results obtained using conventional methods.The analysis methods used in this paper may give information that will have applications for clinical testing. Results confirm and extend knowledge of the effects of repetition rate on AEPs over a range embracing the gamut of responses as traditionally classified, specifically at the beginning stages of natural sleep.

Quasi-steady-state responses were assessed over a wide range of stimulus repetition rates embracing well the traditionally measured transient AEPs (obligatory auditory evoked potentials of all latencies). Repetition rates of ≤10 Hz have received little attention in the context of the ASSR stimulus-response analysis approach which is speculated to provide technical advantages, if not additional information, over more traditional transient stimulus-response paradigms.A measure introduced and defined as the sum of the response at the stimulus frequency and its harmonics. The magnitude of steady-state responses were measured at repetition rates from 0.75 to 80 Hz, using trains of repeated tone-burst stimuli.Twenty-five normal-hearing adults.Results show that the magnitudes of the response across repetition rates are largest at the two lowest rates, following trends expected from the transient AEP literature. Good reliability overall was observed for the harmonic sum.The analysis methods used in this paper may give information that will have application for clinical testing. Of pragmatic importance is that the rate profile could be determined without subjective wave identification and/or interpretation, and thus by a method that is inherently more objective than conventional AEP tests.

A portable speech and signal processing system was developed using a TMS320C6748 Digital Signal Processor (DSP) with two input and output channels with 32 bit Analog-to-Digital (AD) and Digital-to-Analog (DA) converters. Lithium-ion batteries provide up to 10 hours of freestanding operation. The system may also be used while connected to a personal computer (PC). Special boot loading code and an interface protocol was developed in order to allow communications and standardize the transfer of instructions and data between the DSP hardware and PC through a Universal Serial Bus (USB) interface cable. In addition, a PC-based user application interface high-level language dynamic link library was also developed to enable development of a wide range of applications. The library provides functions for user developed applications to communicate with the hardware and be able to upload C language programs into the DSP system. This allows for different programs to be uploaded in order to reconfigure the processing algorithms being executed for any experiment at any time. DSP and PC-based software source code examples provide users with the ability to develop their own user specific applications. Examples were developed to demonstrate the implementation of hearing aid amplification, filtering, and noise cancellation in real time.A portable speech and signal processing system was developed using a TMS320C6748 Digital Signal Processor (DSP) with two input and output channels with 32 bit Analog-to-Digital (AD) and Digital-to-Analog (DA) converters. Lithium-ion batteries provide up to 10 hours of freestanding operation. The system may also be used while connected to a personal computer (PC). Special boot loading code and an interface protocol was developed in order to allow communications and standardize the transfer of instructions and data between the DSP hardware and PC through a Universal Serial Bus (USB) interface cable. In addition, a PC-based user application interface high-level language dynamic link library was also developed to enable development of a wide range of applications. The library provides functions for user developed applications to communicate with the hardware and be able to upload C language programs into the DSP system. This allows for different programs to be uploaded in order to reconfigure the processing a...

Purpose The purpose of the study was to objectively detect age-specific changes that occur in equivalent auditory steady-state responses (ASSRs), corresponding to transient middle- and long-latency auditory evoked potentials as a function of repetition rate and advancing age. Method The study included 48 healthy hearing adults who were equally divided into 3 groups by age: 20–39, 40–59, and 60–79 years. ASSRs were recorded at 7 repetition rates from 40 down to 0.75 Hz, elicited by trains of repeated tone burst stimuli. Results Temporal analysis of middle- and long-latency equivalent ASSRs revealed no appreciable changes in the magnitudes of the response across the age groups. Likewise, the spectral analysis revealed that advancing age did not substantially affect the spectral content of the response at each repetition rate. Furthermore, the harmonic sum was not significantly different across the 3 age groups, between the younger adults versus the combined Older Group Sample 1 and Sample 2, and between the two extreme age groups (i.e., 20–39 vs. 60–79) for the middle- and long-latency equivalent ASSRs. Conclusion Advancing age has no effect on the long-latency equivalent ASSRs; however, aging does affect the middle-latency equivalent ASSRs when the mean age difference is ≥ 40 years.

In this article, we describe an efficient method for testing both auditory receptor and auditory nerve function in a single recording session. Auditory receptor function is tested in response to pure tone, tone burst and click acoustic stimuli (i.e. distortion products of otoacoustic emissions, DPOAE; and auditory-evoked brainstem responses, ABR). The function of the auditory neurons and nerve is measured in response to direct electric current stimulation (i.e. electrically evoked auditory brainstem responses, eABR). All measurements were obtained from anesthetized laboratory rats during single recording sessions using hardware and software stimulation and analysis programs developed by Intelligent Hearing Systems, Miami, FL.

Continuous loop averaging deconvolution (CLAD) is a new general mathematical theory and method developed to deconvolve overlapping auditory evoked responses obtained at high stimulation rates. Using CLAD, arbitrary stimulus sequences are generated and averaged responses deconvolved. Until now, only a few special stimulus series such as maximum length sequences (MLS) and Legendre sequences (LGS) were capable of performing this task. A CLAD computer algorithm is developed and implemented in an evoked potential averaging system. Computer simulations are used to verify the theory and methodology. Auditory brainstem responses (ABR) and middle latency responses (MLR) are acquired from subjects with normal hearing at high stimulation rates to validate and show the feasibility of the CLAD technique.

Purpose To compare a new method for steady-state pattern electroretinogram (PERGx) with a validated method (PERGLA) in normal controls and in patients with optic neuropathy. Methods PERGx and PERGLA were recorded in a mixed population (n = 33, 66 eyes) of younger controls (C1; n = 10, age 38 ± 8.3 years), older controls (C2; n = 11, 57.9 ± 8.09 years), patients with early manifest glaucoma (G; n = 7, 65.7 ±11.6 years), and patients with nonarteritic ischemic optic neuropathy (N; n = 5, mean age 59.4 ± 8.6 years). The PERGx stimulus was a black-white horizontal grating generated on a 14 × 14 cm LED display (1.6 cycles/deg, 15.63 reversals/s, 98% contrast, 800 cd/m2 mean luminance, 25° field). PERGx signal and noise were averaged over 1024 epochs (∼2 minutes) and Fourier analyzed to retrieve amplitude and phase. Partial averages (16 successive samples of 64 epochs each) were also analyzed to quantify progressive changes over recording time (adaptation). Results PERGLA and PERGx amplitudes and latencies were correlated (Amplitude R2 = 0.59, Latency R2 = 0.39, both P < 0.0001) and were similarly altered in disease. Compared to PERGLA, however, PERGx had shorter (16 ms) latency, higher (1.39×) amplitude, lower (0.37×) noise, and higher (4.2×) signal-to-noise ratio. PERGx displayed marked amplitude adaptation in C1 and C2 groups and no significant adaptation in G and N groups. Conclusions The PERGx high signal-to-noise ratio may allow meaningful recording in advanced stages of optic nerve disorders. In addition, it quantifies response adaptation, which may be selectively altered in glaucoma and optic neuropathy. Translational Relevance A new PERG method with increased dynamic range allows recording of retinal ganglion cell function in advanced stages of optic nerve disorders. It also quantifies the response decline during the test, an autoregulatory adaptation to metabolic challenge that decreases with age and presence of disease.

Objective.To document our experiences using a new skull tapping induced Vestibular Evoked Myogenic Potentials (tap VEMPs) technique combined with standard Auditory Vestibular Evoked Myogenic Potentials (AC VEMPs) for advanced clinical assessment of cerebellopontine angle tumor (CPAT) patients.Design and Study Sample.Three patients were selected in order to highlight observations shown in a larger patient population and to show the variability of the findings. Both tap VEMPs and AC VEMPs were acquired from the sternocleidomastoid muscle (SCM) with EMG-based biofeedback and monitoring.Results.The usefulness of VEMPs was demonstrated, indicating the presence of a tumor and contributing additional information as to the involved nerve bundles in two out of the three cases.Conclusion.Due to the sensory organ dependency and related innervations differences, acquiring both AC VEMPs and tap VEMPs is likely to increase the probability of diagnosing CPATs and provide more information on the involved vestibular nerve bundles. This study demonstrates the feasibility of the possible expansion and combination of tap VEMPs and AC VEMPs techniques into a clinical diagnostic battery for advanced assessment of CPAT patients and its contribution as a guideline for the use of tap VEMPs in general.

An innovative acoustic noise canceling method using adaptive Wiener filtering (AWF) was developed for improved acquisition of distortion product otoacoustic emissions (DPOAEs). The system used one microphone placed in the test ear for the primary signal. Noise reference signals were obtained from three different sources: (a) pre-stimulus response from the test ear microphone, (b) post-stimulus response from a microphone placed near the head of the subject and (c) post-stimulus response obtained from a microphone placed in the subject's nontest ear. In order to improve spectral estimation, block averaging of a different number of single sweep responses was used. DPOAE data were obtained from 11 ears of healthy newborns in a well-baby nursery of a hospital under typical noise conditions. Simultaneously obtained recordings from all three microphones were digitized, stored and processed off-line to evaluate the effects of AWF with respect to DPOAE detection and signal-to-noise ratio (SNR) improvement. Results show that compared to standard DPOAE processing, AWF improved signal detection and improved SNR.

The processing of sequential evoked potentials (EPs) is investigated using two-dimensional processing techniques. Two-dimensional EP arrays or images are formed by stacking sequential recordings. Processing is accomplished in the frequency domain by 2-D low-pass filtering using Gaussian filters. Auditory brainstem responses (ABRs), which are the early auditory EPs, are used to investigate the effects of the 2-D filtering on real data. Gaussian filtering improves signal-to-noise ratios by reducing high frequency noise effectively in both intra-EP and inter-EP dimensions. Applications to intra-operative monitoring are simulated with real ABR data.

The authors report a complete automated system for auditory brainstem response (ABR) identification and waveform recognition. The goal was to develop an automated analysis methodology that would facilitate the clinical use of auditory brainstem responses by reducing the time required to manually label and measure absolute and interpeak latencies. The system presented here accomplished this goal, supplying not only threshold information, but also additional diagnostically significant information. In addition, such an automated system will standardize the labeling process, which can vary depending on the labeling preference of individual clinicians. There are currently no commercially available systems capable of labeling ABR peaks or interpreting results originating from a wide range of stimulation intensities. The system developed in this study performs both peak labeling and assessment functions. >

Otoacoustic emission (OAE) screening is perhaps one of the most common diagnostic tools used on both adults and children alike to clinically asses hearing health. However small to moderate middle ear pressures (both positive and negative), which are quite prevalent among the general population, are known to significantly reduce the OAE response specifically among frequencies below 2 kHz. This study focuses on the design and development of a software controlled syringe pump which will be used for the automatic compensation of middle ear pressure. This study reports validating test results which confirm the feasibility of using this system for future clinical trials.

Introduction Surgery of the cerebello-pontine angle tumor (CPAT) is associated with a high risk of damaging such important structures as facial nerve, vestibulocochlear nerve, internal auditory artery, anterior inferior cerebellar artery, and inner ear function, if they escaped earlier damage by[for full text, please go to the a.m. URL], ESBS 2005: Skull Base Surgery: An Interdisciplinary Challenge; 7th Congress of the European Skull Base Society held in association with the 13th Congress of the German Society of Skull Base Surgery

On-line computer methods were developed and evaluated for automated hearing testing with auditory brain stem responses (ABR). The system contained (1) a response recognition unit which recognized the presence or absence of an ABR response and (2) a threshold tracking unit which adjusted stimulus intensity and determined the ABR threshold. Two methods, one nontemplate (variance ratio) and one template (cross-correlation), were evaluated for response recognition while three threshold tracking methods were explored: clinical, Békésy, and PEST (parameter estimation by sequential testing). Both response recognition and threshold tracking units were evaluated by computer simulations for on-line operation using a standard set of experimentally recorded ABRs. The results indicated that while all the response recognition methods were reasonably accurate, their on-line use resulted in significant differences in test efficiency due to differences in tracking methods.

The mode of stimulation employed in newborn screening of the auditory brainstem response has evolved from the clinically standardized supraaural earphone to the tubal insert earphone, to most recently a circumaural earphone developed for this test. Considered here is the need to develop a standard for calibration of such devices for newborn screening applications, in particular. At risk is the prospect of missing the milder degrees of hearing loss, assuming a goal of detecting all clinically-significant congenital hearing losses. Two commercially manufactured test instruments for automated newborn screening were scrutinized via bench testing of sound output from their respective transducers, using a variety of measurements. By convention or design, none of the measurement approaches involved a model of the newborn ear, per se. While it was concluded that the manufacturers' method shows promise, namely as a relatively simple and potentially reliable method of calibration, concerns arose regarding output levels when measured according to both the manufacturers' and the authors' methods. Further work is needed to critically assess calibration methods and to establish, to the extent possible, appropriate norms and validation studies in newborns to provide a better understanding of the actual sound pressure level of the screening stimulus.

The Auditory Steady-state Responses (ASSR) elicited by click stimuli can be utilized for hearing screening as is traditionally done with click-evoked Auditory Brainstem Responses (ABR). In a typical ASSR or ABR hearing screening, several recordings at different intensities are required to find the response threshold. In this study the use of binaural click stimulus with time ramping intensity produces dual-ear evoked potentials in only one recording session, decreasing significantly the recording time. To achieve this performance a one second sweep consisting of repetitive click stimuli, with logarithmically ramping up intensity, is presented to one or both ears simultaneously. Unique repetition frequencies for each ear are used in order to differentiate the responses coming from each ear. The stimuli sweep is repeated and the EEG data corresponding to each sweep is averaged until a pre-specified residual noise level is achieved. Hilbert-transform-based envelope detection filters in the time domain are used to estimate the signal and noise energy around the main stimulation rate. Because the stimulus time-intensity functions are known, thresholds can be estimated from the response onset time position by estimating the significance of the signal to noise ratio. Preliminary results indicate a strong agreement of the obtained thresholds with behavioral thresholds.

To investigate the use of transtympanic electrocochleography (TT-ECochG) analyzed on-line by a detector strategy software that made possible automatic extraction of TT-ECochG components intraoperatively in real-time domain.Fifteen patients with cerebellopontine angle tumor among 50 patients were included in this study.All subjects were operated on via middle fossa or retrosigmoid approach. Pure-tone average (PTA) was measured at 0.5, 1.0, and 2.0 kHz, and calculations were performed before and after surgery. Auditory function was monitored intraoperatively via TT-ECochG, and analyzed data were displayed on-line.TT-ECochG changes in morphology were described. Postoperative PTA elevation level correlated with TT-ECochG morphology changes occurring intraoperatively.Analyzed on-line, TT-ECochG data were displayed as first negative peak of compound action potential amplitude and latency in time domain every 3 to 5 seconds. A good correlation between postoperative PTA elevation and TT-ECochG morphology changes was showed (Spearman rank test, R = +0.93; t(N-2) = 9.00; p0.0001).TT-EcochG seemed to effectively mirror even minimal changes in auditory function during intraoperative monitoring in real-time domain. Developed strategy of on-line analysis makes the intraoperative hearing status assessment faster and easier.

This chapter contains sections titled: Introduction Methodology Results Discussion References

An automated Auditory Brainstem Response (ABR) peak identification and labelling system is developed and evaluated. The system uses a set of matched filters and a rule base for on-line peak labelling. The matched filters are designed to reflect the spectral and biphasic characteristics of the ABR peaks. The rules are designed to identify ABR peaks based on the latencies and amplitudes of the peaks found in the matched filter output buffers. The system is capable of automatic generation of latency-intensity functions. The algorithm was tested using 168 ABRs from four adults, yielding only 2 incorrectly labelled recordings.

In this study, Auditory Steady State Responses (ASSR) to 100 /spl mu/sec clicks and 4 msec cochlear chirps are recorded in adult subjects at repetition rates of 20 to 100 Hz in 10 Hz increments. Response characteristics of ASSRs are compared in the frequency domain. Results show that response amplitudes to both stimuli peak in the proximity of 40 Hz and 80 Hz, but chirps generate responses with larger amplitudes at all repetition rates. The responses at 40 Hz repetition rates for both clicks and chirps are larger than the corresponding responses at 80 Hz stimuli in awake adults. The 40 Hz responses, however, show greater variability than the 80 Hz responses depending on the subject's state of consciousness. The predictions of the ASSR waveforms at each repetition rate were then synthesized by superimposing the suitably shifted Middle Latency Response (MLR) waveforms that were recorded during the same session with a stimulus repetition rate of 10 Hz for both click and chirp recordings. This part of the study was undertaken to Investigate the validity of the hypothesis which states that the steady state responses are simply the linear additions of transient MLRs. The results showed that the synthesized waveforms resembled the real recordings to some extent, but consistently had larger amplitudes. This difference is assumed to be a result of the adaptation effects of higher stimulus rates.

A system capable of comprehensive and detailed monitoring of the cochlea and the auditory nerve during intraoperative surgery was developed. The cochlear blood flow (CBF) and the electrocochleogram (ECochGm) were recorded at the round window (RW) niche using a specially designed otic probe. The ECochGm was further processed to obtain cochlear microphonics (CM) and compound action potentials (CAP).The amplitude and phase of the CM were used to quantify the activity of outer hair cells (OHC); CAP amplitude and latency were used to describe the auditory nerve and the synaptic activity of the inner hair cells (IHC). In addition, concurrent monitoring with a second electrophysiological channel was achieved by recording compound nerve action potential (CNAP) obtained directly from the auditory nerve. Stimulation paradigms, instrumentation and signal processing methods were developed to extract and differentiate the activity of the OHC and the IHC in response to three different frequencies. Narrow band acoustical stimuli elicited CM signals indicating mainly nonlinear operation of the mechano-electrical transduction of the OHCs. Special envelope detectors were developed and applied to the ECochGm to extract the CM fundamental component and its harmonics in real time. The system was extensively validated in experimental animal surgeries by performing nerve compressions and manipulations.

In this study, a new monitoring system is developed to measure cochlear blood flow (CBF) and electrocochleography (ECochG) during transient ischemic episodes of the cochlea. A newly designed otic probe was used for the simultaneous recordings of laser-Doppler CBF and ECochG directly from the round window (RW). The probe enabled the recording of high amplitude compound action potentials (CAP) and cochlear microphonics (CM) with few averages. Experiments were conducted on rabbits to generate episodes of cochlear ischemia by using timed compressions of the internal auditory artery (IAA). The computer monitoring system extracted and measured CAP and CM components from ECochG in real-time. Results indicate that CM and CAP generally followed CBF during compressions and releases of IAA. Both CBF values and CAP amplitudes showed an overshoot following the reperfusion. CAP amplitude measures were found to be very sensitive to ischemia showing very rapid amplitude, latency and morphological changes. CM amplitude decreased more slowly than the CAP and CBF. Simultaneous recordings of CBF and ECochG using the otic probe provide a valuable neuromonitoring tool to investigate the dynamic behavior of the cochlea during ischemia.

Problem: To investigate the utility of cochlear microphonics (CM) measured directly from the cerebello-pontine angle region (CPA) in intraoperative monitoring of auditory function during reversible episodes of cochlear ischemia. Methods: Five young rabbits were used in this study. The round window (RW) visualization and the VIII nerve complex with internal auditory artery (IAA) approach via a sub-occipital posterior craniotomy were described in our earlier publications. Laser-Doppler cochlear blood flow (LD-CBF), CM, and compound action potentials (CAP) were measured using a specially designed probe placed at the RW niche. Simultaneously, CM and CAP were recorded directly from the CPA region on the same side using a needle electrode situated close to the eight nerve structure. Results: In all ears, following IAA compression LD-CBF was reduced to a background level. The CMs measured from the RW niche were reduced very quickly correlating well with LD-CBF. Then, following IAA release, both CBF and CM amplitudes recovered quickly to the preblockage level. For all cochlear ischemia-reperfusion episodes good correlation was obtained between CM amplitude and LD-CBF (Pearson correlation test: R = 0.85 to 0.95; P Conclusion: CMs measured directly from CPA region effectively mirrored cochlear ischemia-reperfusion episodes and corresponding cochlear reversible dysfunction. Significance: Such a strategy may serve as an effective tool for indirect intraoperative monitoring of the cochlear function and changes in the inner blood supply. Support: NIH 2R44DC04344-02, University of Miami Ear Institute.

A neuromonitoring system using compound action potential (CAP) and cochlear blood flow (CBF) is developed to assess the functional status of the cochlea during hypoxia. The system uses a specially designed optic probe capable of acquiring CAP and CBF signals and modules to process and display these signals. The system is tested in rabbits by creating cochlear hypoxia by manual compression of the auditory nerve and acoustic artery. Results show that CAP and CBF measurements can provide almost real time information on the status of the cochlea under compromising situations.

The aim of this project is the development of a microsurgical laser Doppler (LD) probe that simultaneously monitors blood flow and Electrocochleography (ECochG) from the round window of the ear. The device will prevent neurosensory hearing loss during acoustic neuroma surgery by preventing damage to the internal auditory nerve and to the cochlear blood flow supply. A commercially available 0.5 mm diameter Laser-Doppler velocimetry probe (LaserFlo, Vasamedics) was modified to integrate an ECochG electrode. A tube for suction and irrigation was incorporated into a sheath of the probe shaft, to facilitate cleaning of the round window (RW) and allow drug delivery to the round window membrane. The prototype microprobe was calibrated on a single vessel model and tested in vivo in a rabbit model. Preliminary results indicate that the microprobe was able to measure changes in cochlear blood flow (CBF) and ECochG potentials from the round window of rabbits in vivo. The microprobe is suitable for monitoring cochlear blood flow and auditory cochlear potentials during human surgery.

Although diagnostic testing with auditory evoked potentials (EPs) has become routine, quantitative measurements of signal and noise are still lacking. In this study, current signal, power, noise power, and signal-to-noise ratio (SNR) estimation formulas are reviewed and applied to auditory brainstem response averaging. Single-sweep responses to individual sound stimuli are recorded and estimation formulas are evaluated during off-line averaging under various sound level and noise conditions. The results show that the quality of the averaged EP can be quantitatively assessed by the continuous display of the SNR and residual noise estimates during the averaging process. This method also allows the study of different types of averaging techniques to improve EP response acquisition.

Methods and instrumentation were developed to monitor cochlea and auditory function during surgery. The system allows real time assessment of the cochlear function during auditory nerve manipulation. A specially designed optic probe, placed on the round window (RW) niche, enables simultaneous acquisition of cochlear blood flow (CBF) and electrocochleogram (ECochG). We developed the acquisition paradigms, signal processing methods and implement them in a computational platform. The neuromonitoring system performs an automatic extraction and analysis of cochlear microphonics (CM), compound action potentials (CAP) and sura mating potential (SP). The system uses envelope detection filters to detect the amplitude of the CM. The CAP signal is processed with zero phase shift spectral filters, tuned to enhance the action potential onset, which is sometimes embedded within the sura mating potential. An automatic peak detection and tracking algorithm is then applied to extract latency and amplitude of CAPs. Long-term assessment of the monitoring system was performed during experimental animal surgeries. The system allowed detailed study of the dynamics of CM, CAP and CBF during nerve manipulation and compression.

A fiber tract model for the generation of auditory brain‐stem responses (ABRs) is developed using volume conducted potentials in a spherical conducting medium. This model proposes that the fast components of the ABR are generated by the synchronized propagation of the action potentials traveling along the auditory brain‐stem pathways. The model represents an action potential with up to 100 current dipoles traveling along a pathway corresponding to a known auditory brain‐stem tract. Coordinates of the major fiber tracts are obtained from human brain atlases and adapted to a spherical head model. Computations assuming classical interconnections between brain‐stem nuclei show that such synchronously propagating action potentials can generate waveforms similar to recorded ABRs. According to this model, positive peaks correspond to the depolarizing wave front of the action potential while negative valleys are generated with the repolarizing phase.